The present invention relates to a method for stacking parts that are comprised of thermoplastic plastic, and that have been molded and punched out of a heated film strip in a molding/punching tool, then transferred into an intermediate-storage cage, either directly from the tool or by a transfer device, then transferred as a stack into a stacking cage that is held on a carrier, and finally conveyed with this cage to a stack-removal station where the stacks of parts are removed. The invention further relates to an apparatus for executing the method.
The parts, which are molded and punched in a thermoforming machine by a combination molding/punching tool, are transferred into stacking magazines after being ejected from the molding/punching tool. This can be effected directly, as described in DE 33 46 628 C2, in which the mold floor of the tool is displaced, which transfers the parts into the stacking magazines, where they are then retained. It can also be effected indirectly through the interposing of a transfer device in the form of a rotating head (DE 198 52 359 A1) or a catch plate (DE 198 12 414 A1).
A problem associated with these methods is emptying the stacks that form in the stacking magazines once they reach a specific length or number of items, and transporting the stacks to a finishing device or a packaging device. This is particularly the case with multiple rows of molding/punching tools.
DE 198 48 628 A1 proposes to transfer the parts that are stacked in a mobile catch plate into a mobile stacking basket once a predetermined number of items has been reached. The basket then transports the stacks to an unloading station, where they are pushed out of the basket by rows onto a transverse conveyor belt. A drawback of this method is the time-consuming process of transferring the stacks into the displaceable stacking basket by displacing the catch plate. Certain strokes must be executed with a limited speed due to the forces of gravity and the forces acting on the parts during the transfer (risk of deformation). This problem must be solved with a precisely-adapted change in speed, which is complicated, and is limited at high cycle numbers, so it limits the cycle number. The cycle number is increasing continuously in modern machines. However, the problem lies in stacking and handling the stacks, and this condition limits the cycle number.
The known apparatus allows the stacks to be transferred lying down onto a horizontally running transverse conveyor belt. Stacks of relatively flat parts, such as lids and dishes, tend to drift apart in this position, and thus cannot be further handled. These stacks must be transported standing up, for which the apparatus is not suited. A further disadvantage is that the catch plate can move in the stacking direction, and therefore impedes or precludes the mounting of certain devices that reliably prevent the first stacked parts from tipping.